From: "Md. Islam" mislam4@kent.edu
[ Upstream commit 043e337f555e610ad8237fd23522d97c968d72b9 ]
In Kernel 4.15.0+, Netem does not work properly.
Netem setup:
tc qdisc add dev h1-eth0 root handle 1: netem delay 10ms 2ms
Result:
PING 172.16.101.2 (172.16.101.2) 56(84) bytes of data. 64 bytes from 172.16.101.2: icmp_seq=1 ttl=64 time=22.8 ms 64 bytes from 172.16.101.2: icmp_seq=2 ttl=64 time=10.9 ms 64 bytes from 172.16.101.2: icmp_seq=3 ttl=64 time=10.9 ms 64 bytes from 172.16.101.2: icmp_seq=5 ttl=64 time=11.4 ms 64 bytes from 172.16.101.2: icmp_seq=6 ttl=64 time=11.8 ms 64 bytes from 172.16.101.2: icmp_seq=4 ttl=64 time=4303 ms 64 bytes from 172.16.101.2: icmp_seq=10 ttl=64 time=11.2 ms 64 bytes from 172.16.101.2: icmp_seq=11 ttl=64 time=10.3 ms 64 bytes from 172.16.101.2: icmp_seq=7 ttl=64 time=4304 ms 64 bytes from 172.16.101.2: icmp_seq=8 ttl=64 time=4303 ms
Patch:
(rnd % (2 * sigma)) - sigma was overflowing s32. After applying the patch, I found following output which is desirable.
PING 172.16.101.2 (172.16.101.2) 56(84) bytes of data. 64 bytes from 172.16.101.2: icmp_seq=1 ttl=64 time=21.1 ms 64 bytes from 172.16.101.2: icmp_seq=2 ttl=64 time=8.46 ms 64 bytes from 172.16.101.2: icmp_seq=3 ttl=64 time=9.00 ms 64 bytes from 172.16.101.2: icmp_seq=4 ttl=64 time=11.8 ms 64 bytes from 172.16.101.2: icmp_seq=5 ttl=64 time=8.36 ms 64 bytes from 172.16.101.2: icmp_seq=6 ttl=64 time=11.8 ms 64 bytes from 172.16.101.2: icmp_seq=7 ttl=64 time=8.11 ms 64 bytes from 172.16.101.2: icmp_seq=8 ttl=64 time=10.0 ms 64 bytes from 172.16.101.2: icmp_seq=9 ttl=64 time=11.3 ms 64 bytes from 172.16.101.2: icmp_seq=10 ttl=64 time=11.5 ms 64 bytes from 172.16.101.2: icmp_seq=11 ttl=64 time=10.2 ms
Reviewed-by: Stephen Hemminger stephen@networkplumber.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- net/sched/sch_netem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 2aeca57f9bd0..73c4bea821cb 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -327,7 +327,7 @@ static s64 tabledist(s64 mu, s32 sigma,
/* default uniform distribution */ if (dist == NULL) - return (rnd % (2 * sigma)) - sigma + mu; + return ((rnd % (2 * sigma)) + mu) - sigma;
t = dist->table[rnd % dist->size]; x = (sigma % NETEM_DIST_SCALE) * t;